1. Field of the Invention
The present invention is directed to a shock wave generator for use in an extracorporeal lithotripter, and in particular to such a shock wave generator having a membrane formed of electrically conductive material disposed opposite the coil and terminating a volume filled with fluid.
2. Description of the Prior Art
German OS No. 33 12 014 discloses a shock wave generator having a membrane disposed parallel to the coil. The shock waves are generated by connecting the coil to a high voltage supply, containing a capacitor charged to several kilovolts, for example, 20 kV. The energy stored in the capacitor discharges rapidly into the coil, causing the coil to rapidly generate a magnetic field. At the same time, a current is induced in the membrane, this current having an opposite plurality to the current flowing in the coil, and consequently generating an opposing magnetic field, which causes the membrane to rapidly move away from the coil. The shock wave thereby generated in the adjacent volume filled with liquid, for example water, is focussed with known means to the calculi, for example kidney stones, disposed within the body of a life form, and causes disintegration thereof.
In order to achieve the highest possible conversion of the electrical energy output of the high voltage supply into shock energy, it is necessary in such known shock wave generators to attach the membrane as close as possible to the coil. Due to the difference in potential necessarily existing between the coil and the membrane, however, this is only possible within certain limits because a minimum spacing must be observed in order to avoid arcing between the membrane and the coil. Arcing deteriorates the effectiveness of the shock wave generator, and also leads to damage of the membrane, the latter lessening the useful life thereof. In conventional shock wave generators, therefore, the spacing between the membrane and the coil must be selected so as to maintain an adequate useful life of the membrane, thereby necessarily resulting in an unsatisfactory efficiency in the conversion of electrical energy into shock energy.